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| TOP > Ball Technologies > Why Spherical > Today's Technology |
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| Semiconductor manufacturing today is a costly, fragmented and inefficient process that takes place in three stages: material processing, wafer fabrication, and assembly testing. Material Processing: Creating silicon wafers requires creating rod-form polycrystalline semiconductor material; precisely cutting ingots from the rods; cleaning and drying the cut ingots; manufacturing a large single crystal from the ingots by melting them in a quartz crucible; grinding, etching, and cleaning the surface of the crystal; cutting, lapping, and polishing wafers from the crystal to a mirror-smooth finish; and heat-processing the wafers. Because of semiconductor resistivity, only around one-third of the original rod is of high enough quality to be used in making integrated circuits. The remainder can often be re-processed and used for products that do not require such high purity, such as silicon solar cells. Wafer Fabrication: Wafer processing comprises eight basic process steps, each of which may be repeated many times, depending on the particular chip being manufactured. In deposition, an insulating layer is deposited on the wafer that can be patterned to form circuit elements. During ion implantation, dopants or other impurities are introduced into a wafer's surface to create silicon crystals that conduct electricity. |
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| In the Photo-lithography/ patterning phase the actual circuits are created on the wafer. Photo masks expose a chemical coating, called photo resist, to ultraviolet light. Machines called steppers are used to imprint circuit patterns onto wafers. [Note: Today's conventional CMOS circuit requires 22 mask levels; creating a "mixed-signal" or BiCMOS device requires an average of additional 10 mask levels.] During the etching stage, wafers are moved to a plasma reactor where electrically excited gases etch the surface into the pattern defined in the photolithography process. After etching, wafers are cleaned. During diffusion, impurities are baked onto the wafer, altering its electrical characteristics to create separate regions with excess negative or positive charge. The impurities are diffused along lines defined in the photolithography process and etching processes. During metalization, interconnections are formed on each of the integrated circuits being produced on every wafer. Metalization is also used for bond pads that interconnect a chip to other components on a printed circuit board. Toward final wafer fabrication, each wafer is tested to determine defective components, and a protective coating of silicon nitride is applied. The final processing step is multiprobe testing, in which each integrated circuit on a wafer is electrically tested to determine whether it is ready for final assembly, bonding, and packaging. Assembly and Test: The final phase of the integrated circuit manufacturing process involves cutting the finished wafers into individual chips; wire-bonding the chips onto a lead frame; encapsulating chips in plastic or ceramic molding; and forming leads to interface the chip to a printed circuit board. |